There are known biological object detectors which sense a temperature by means of an infrared sensor or the like and determine whether or not there is a biological object at a predetermined position, on the basis of the sensed temperature (e.g., see Patent Document 1).
Further, there are known vehicle seat occupancy detectors used for seat belt non-wearing warning systems. Such a seat occupancy detector senses a weight applied to a seating surface of a seat and determines whether or not an occupant is seated on the seat, on the basis of the sensed weight.